Modularized direct current transformer and control system

Abstract

The invention relates to the technical field of power electronics, in particular to a modular direct-current transformer and a control system. The modularized direct-current transformer comprises at least two voltage self-balancing modules and at least one DAB module, a voltage self-balancing module serves as an input module, a primary port of the input module is connected with a low-voltage side, and a secondary port of the input module is connected with the DAB module in parallel; the voltage self-balancing module of the non-input module serves as a transmission module, and a primary port of the transmission module is connected with a primary port of the input module in series and used for being connected with a high-voltage side; a secondary port of the transmission module is connected with the DAB module; and the voltage self-balancing module is used for balancing the internal voltage, so that the voltage balancing can be conveniently realized, the voltage balancing difficulty is reduced, the energy transmission efficiency is improved, and the problem that the voltage balancing of the existing modular direct current transformer is complicated is solved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a modular direct current transformer and a control system. Background Art

[0002] As energy crisis and environmental problems become increasingly prominent, the research on renewable energy has gradually become a focus. Among various types of renewable energy, wind resources are abundant, especially offshore wind power, which has great potential. Therefore, offshore wind power has been widely used, and wind turbines used in offshore wind power have also been developed on a large scale. However, due to the large-scale development of wind turbines, the offshore distance of wind farms has gradually increased, resulting in an increase in the charging current of submarine cables, increasing the operating cost and system loss of wind power systems, and reducing system efficiency. Therefore, the existing technology proposes to use a pure DC system (including DC transmission and collection systems) without reactive power loss and frequency stability problems to achieve grid connection of long-distance wind farms, improve system efficiency, and reduce system losses.

[0003] In a pure DC system, the DC transformer is a key device that connects the fan and the medium voltage collection network. It is used to achieve conversion between different DC voltage levels and has application requirements of high transformation ratio and large capacity. In order to achieve high voltage applications, one solution is to expand the DC / DC converter used in low voltage environment to medium and high voltage environment by series connection. However, after the IGBT in the DC / DC converter is connected in series, the voltage balancing becomes complicated and it is difficult to achieve voltage balancing. Another solution is to use a modular multi-level DC transformer such as Buck-MMDCT. Although this solution avoids the cumbersome problems caused by the series connection of devices, in actual applications, it needs to inject AC circulating current to achieve energy balance of sub-modules, which makes the control strategy complicated and increases losses. Therefore, how to construct a new DC transformer to reduce the difficulty of voltage balancing and improve energy transmission efficiency has become an urgent problem to be solved. Summary of the invention

[0004] The present invention provides a modular direct current transformer and a control system, which are used to reduce the difficulty of voltage balancing and improve energy transmission efficiency.

[0005] In one aspect, the present invention provides a modular DC transformer, comprising: at least two voltage self-balancing modules and at least one DAB module;

[0006] Using one of the voltage self-balancing modules as an input module, the primary port of the input module is connected to the low voltage side, and the secondary port of the input module is connected in parallel with the DAB module;

[0007] The voltage self-balancing module of the non-input module is used as a transmission module, and the primary port of the transmission module is connected in series with the primary port of the input module for connecting to the high-voltage side; the secondary port of the transmission module is connected to the DAB module;

[0008] The voltage self-balancing module is used to balance the voltage inside it.

[0009] Optionally, the voltage self-balancing module includes: a voltage balancing component, a first DC capacitor, a second DC capacitor and an output capacitor;

[0010] The first DC capacitor, the second DC capacitor, and the output capacitor are connected in series in sequence to form the primary port; the two ends of the output capacitor are the secondary ports;

[0011] The voltage balancing component is respectively connected to both ends of the first DC capacitor, both ends of the output capacitor, and both ends of the second DC capacitor, and is used to balance the voltage of the first DC capacitor, the voltage of the second DC capacitor, and the voltage of the output capacitor.

[0012] Optionally, the voltage balancing component includes a first resonant branch, a second resonant branch, a first half-bridge submodule, a second half-bridge submodule, and a third half-bridge submodule;

[0013] The first half-bridge sub-module is connected in parallel with the first DC capacitor;

[0014] The second half-bridge submodule is connected in parallel with the output capacitor;

[0015] The third half-bridge sub-module is connected in parallel with the second DC capacitor;

[0016] The first half-bridge submodule, the second half-bridge submodule, and the third half-bridge submodule are connected in series;

[0017] The first resonant branch is connected to the first half-bridge sub-module and the second half-bridge sub-module respectively;

[0018] The second resonant branch is connected to the second half-bridge sub-module and the third half-bridge sub-module respectively.

[0019] Optionally, the first resonant branch includes a first resonant inductor and a first resonant capacitor; one end of the first resonant inductor and one end of the first resonant capacitor are connected in series;

[0020] The other end of the first resonant capacitor is connected to the first half-bridge sub-module;

[0021] The other end of the first resonant inductor is connected to the second half-bridge sub-module.

[0022] Optionally, the second resonant branch includes a second resonant inductor and a second resonant capacitor; one end of the second resonant inductor and one end of the second resonant capacitor are connected in series;

[0023] The other end of the second resonant capacitor is connected to the second half-bridge sub-module;

[0024] The other end of the second resonant inductor is connected to the third half-bridge sub-module.

[0025] Optionally, the first half-bridge submodule includes a first semiconductor power switch device and a second semiconductor power switch device;

[0026] The first end of the first semiconductor power switch device is connected to one end of the first DC capacitor; the second end of the first semiconductor power switch device is connected to the other end of the first resonant capacitor and the first end of the second semiconductor power switch device respectively;

[0027] The second end of the second semiconductor power switch device is connected to the second half-bridge sub-module and the other end of the first DC capacitor respectively.

[0028] Optionally, the second half-bridge submodule includes a third semiconductor power switch device and a fourth semiconductor power switch device;

[0029] The first end of the third semiconductor power switch device is respectively connected to one end of the output capacitor and the second end of the second semiconductor power switch device; the second end of the third semiconductor power switch device is respectively connected to the other end of the first resonant inductor, the other end of the second resonant capacitor, and the first end of the fourth semiconductor power switch device;

[0030] The second end of the fourth semiconductor power switch device is connected to the third half-bridge sub-module and the other end of the output capacitor respectively.

[0031] Optionally, the third half-bridge submodule includes a fifth semiconductor power switch device and a sixth semiconductor power switch device;

[0032] The first end of the fifth semiconductor power switch device is respectively connected to one end of the second DC capacitor and the second end of the fourth semiconductor power switch device; the second end of the fifth semiconductor power switch device is respectively connected to the other end of the second resonant inductor and the first end of the sixth semiconductor power switch device;

[0033] The second end of the sixth semiconductor power switch device is connected to the other end of the second DC capacitor.

[0034] The present invention also provides a control system, characterized in that it includes a controller and the modular DC transformer as described above;

[0035] The controller is respectively connected to the DAB module and the voltage self-balancing module in the modular DC transformer.

[0036] Optionally, the controller is connected to a first half-bridge sub-module, a second half-bridge sub-module, and a third half-bridge sub-module in the voltage self-balancing module.

[0037] On the other hand, the present invention provides a modular DC transformer, comprising at least two voltage self-balancing modules and at least one DAB module; one of the voltage self-balancing modules is used as an input module, the primary port of the input module is connected to the low-voltage side, and the secondary port of the input module is connected in parallel with the DAB module; the voltage self-balancing module that is not an input module is used as a transmission module, the primary port of the transmission module is connected in series with the primary port of the input module for connection to the high-voltage side; the secondary port of the transmission module is connected to the DAB module; the voltage self-balancing module is used to balance the voltage inside it.

[0038] It can be seen from the above technical solutions that the present invention has the following advantages:

[0039] In the present invention, the voltage self-balancing module has the characteristics of self-balancing, and can adjust the voltage inside it by itself to achieve the effect of voltage balancing in the module. In addition, in the present invention, one of the voltage self-balancing modules is used as an input module, and the remaining voltage self-balancing modules are used as transmission modules, and the primary port of the input module is connected to the low-voltage side, and the primary ports of all the voltage self-balancing modules are connected in series in sequence for connection with the high-voltage side, and the secondary port of the input module is connected to the DAB module, and the DAB module is connected to the secondary port of the transmission module, so that the topology of the entire DC transformer constitutes a self-coupling structure, so that energy can be transferred from the secondary port of the input module to other modules, and energy balance between modules is achieved. Moreover, based on the topological structure provided by the present invention, energy can be directly transferred between the input stage and the DAB module, thereby improving the energy transmission efficiency. It can be seen that the modular DC transformer provided by the present invention can realize voltage balancing more conveniently, reduce the difficulty of voltage balancing, improve energy transmission efficiency, and solve the problem of complex voltage balancing in the existing modular DC transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0041] Figure 1 A schematic diagram of the structure of a modular DC transformer provided by an embodiment of the present invention;

[0042] Figure 2 A schematic diagram of the structure of a voltage self-balancing module provided in an embodiment of the present invention;

[0043] Figure 3 Another structural schematic diagram of a modular DC transformer provided by an embodiment of the present invention;

[0044] Figure 4 A schematic diagram of the principle of a voltage self-balancing module provided in an embodiment of the present invention, wherein (a) is a schematic diagram of the principle of one working mode of the voltage self-balancing module; (b) is a schematic diagram of the principle of another working mode of the voltage self-balancing module;

[0045] Figure 5 A waveform diagram of a voltage self-balancing module provided in an embodiment of the present invention;

[0046] Figure 6 A schematic diagram of a simulation waveform of a voltage self-balancing module provided in an embodiment of the present invention;

[0047] Figure 7 Another schematic diagram of simulation waveforms of the voltage self-balancing module provided by an embodiment of the present invention;

[0048] Figure 8 A schematic diagram of the structure of a control system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to avoid injecting AC circulating current, the prior art constructs an energy balance channel structure between the modules of Buck-MMDCT, which provides an additional control variable for energy balance and allows the power loop and the energy balance loop to be controlled separately and independently. However, this mode requires multiple switching devices. In order to avoid adding too many switching devices, the prior art also proposes to improve the energy channel, use DC capacitors to transmit DC current, and build auxiliary branches between modules to transfer energy to balance energy without increasing the number of devices. However, in this solution, since the energy is still transmitted step by step, the corresponding losses will also increase, reducing the energy transmission efficiency. Therefore, how to construct a new DC transformer to reduce the difficulty of voltage balancing and improve energy transmission efficiency has become an urgent problem to be solved.

[0050] In order to solve the above problems, an embodiment of the present invention provides a modular DC transformer and a control system, which are used to reduce the difficulty of voltage balancing and improve energy transmission efficiency.

[0051] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] See also Figure 1 A modular DC transformer provided by the present invention comprises: at least two voltage self-balancing modules 3RSC and at least one DAB module; one voltage self-balancing module 3RSC is used as an input module, the primary port of the input module is connected to the low-voltage side, and the secondary port of the input module is connected in parallel with the DAB module; the voltage self-balancing module 3RSC which is not an input module is used as a transmission module, the primary port of the transmission module is connected in series with the primary port of the input module, and is used to be connected to the high-voltage side; the secondary port of the transmission module is connected to the DAB module; the voltage self-balancing module 3RSC is used to balance the voltage inside it.

[0053] It should be noted that two resonant circuits for balancing voltage are provided in the voltage self-balancing module 3RSC, and the output voltage of the secondary port is adjusted so that the voltage of the primary port is three times the voltage of the secondary port, so that the voltage inside the module is balanced. The DAB module refers to a dual active bridge (Dual Active Bridge) module, which can realize bidirectional energy transmission and voltage level conversion. Among them, the dual active bridge includes two full-bridge circuits, a high-frequency transformer, and a filter capacitor, wherein the two full-bridge circuits are respectively located on the input side and the output side of the high-frequency transformer, wherein the full-bridge circuit located on the input side is used to convert the input DC voltage into an AC voltage, and the transformer is used to convert the received AC voltage into an AC voltage suitable for the voltage level of the output side and output it, and the full-bridge circuit located on the output side is used to convert the received AC voltage into a DC voltage output. In this embodiment, the DAB module is used to perform power interaction between the input module and the transmission module. Among them, the low-voltage side is used to provide input voltage for the modular DC transformer, and the modular DC voltage converts the input voltage into a corresponding output voltage and outputs it to the high-voltage side.

[0054] In the topology of this embodiment, each voltage self-balancing module 3RSC is provided with a primary port and a secondary port, and both the primary port and the secondary port have two ends. In this embodiment, one of the voltage self-balancing modules 3RSC is used as an input module, and the remaining voltage self-balancing modules 3RSC are used as transmission modules.

[0055] like Figure 1 As shown, this example uses 3RSC-0 and 3RSC-x (x=1,2…n) to number each voltage self-balancing module 3RSC, 3RSC-0 is the input module, 3RSC-1 to 3RSC-n are the transmission modules, where n is a positive integer. In this embodiment, the primary port of the input module 3RSC-0 is used as the low-voltage side input interface, and its two ends are connected to the low-voltage side V dc1 Connect the primary ports of all transmission modules 3RSC-1 to 3RSC-n in series and connect them to one end of the input module 3RSC-0. One end of the primary port of the transmission module 3RSC-n far away from one end of the input module 3RSC-0 and one end of the primary port of the input module 3RSC-0 are connected to the high voltage side V dc2 Therefore, in this embodiment, the low voltage side V dc1 and high voltage side V dc2 The primary port of the common input module 3RSC-0 is connected to one end of the DAB module, and the other end of the DAB module is connected to the transmission module.

[0056] The number of DAB modules is the same as that of transmission modules. When there are multiple DAB modules, the two-end lead wires of the secondary port of the input module 3RSC-0 are used as the DC bus V bus , each DAB module is connected to the DC bus V bus On, the input voltages received by each DAB module are equal. Moreover, since each DAB module is connected to the secondary port of each transmission module in a one-to-one correspondence, in practical applications, the output voltages of each DAB module can be controlled to be equal, so that the voltages of the secondary ports of each transmission module are equal. Since each transmission module has a self-balancing function, the voltage of the primary port of each transmission module is three times the voltage of the secondary port. Therefore, when the voltages of the secondary ports of each transmission module are equal, the voltages of the primary ports of each transmission module are also equal, thereby achieving energy balance between modules. Therefore, the entire topology of the modular DC transformer of this embodiment is a self-coupling structure, so that energy can be transferred from the secondary port of the input module 3RSC-0 to other modules, achieving energy balance between modules, and based on the topological structure provided by the present invention, energy can be directly transferred between the input stage and the DAB module, thereby improving energy transmission efficiency.

[0057] Based on the multi-modular DC transformer provided in this embodiment, in practical applications, different voltage transformation ratios can be achieved by changing the number of transmission modules and DAB modules, without the need to inject AC commutation and complex voltage equalization strategies. Moreover, the voltage self-balancing module 3RSC has the characteristic of self-balancing, so in actual operation, it is only necessary to control the output voltage of the DAB module to achieve overall voltage control. Moreover, in the modular DC transformer constructed in this embodiment, the energy between the modules can be transmitted through the DC bus, the overall transmission loss is small, and the transmission efficiency is high. It can be seen that the modular DC transformer provided by the present invention can achieve voltage balancing more conveniently, reduce the difficulty of voltage balancing, improve the energy transmission efficiency, and solve the problem of complex voltage balancing in existing modular DC transformers.

[0058] In a specific embodiment, see Figure 2 The voltage self-balancing module includes: a voltage balancing component 21, a first DC capacitor C p0 , the second DC capacitor C n0 and output capacitor C o0 ;

[0059] The first DC capacitor C p0 , the second DC capacitor C n0 , output capacitor C o0 Connect in series to form a primary port; output capacitor C o0 The two ends of are secondary ports;

[0060] The voltage equalization components 21 are respectively connected to the first DC capacitors C p0 The two ends of the output capacitor C o0 The two ends of the second DC capacitor C n0 The two ends of the capacitor are connected to balance the first DC capacitor C p0 The voltage of the second DC capacitor C n0 The voltage of the output capacitor C o0 voltage.

[0061] It should be noted that the voltage equalization component 21 and the first DC capacitor C p0 A resonant circuit is formed, wherein the voltage equalizing component 21 and the second DC capacitor C n0 Another resonant circuit is formed. Among them, the first DC capacitor C p0 and the second DC capacitor C n0 The electric energy can be output to the voltage balancing component 21, and the voltage balancing component 21 can output the electric energy to the output capacitor C o0 Charging and regulating the output capacitor C o0 The voltage across the two ends makes the first DC capacitor C p0 , the second DC capacitor C n0 , output capacitor C o0The voltage at both ends is stabilized at a preset voltage value, thereby achieving voltage balance within the module.

[0062] Specifically, the voltage self-balancing module has two working modes, and the two working modes are operated alternately in half a cycle. In one working mode, the voltage balancing component 21 and the first DC capacitor C p0 The loop conduction, voltage balancing component 21 and output capacitor C o0 The circuit is turned on, where the first DC capacitor C p0 Output power to the voltage balancing component 21, and the voltage balancing component 21 outputs power to the output capacitor C o0 In another working mode, the voltage equalization component 21 and the second DC capacitor C n0 The loop is turned on, and the resistance balancing component and the output capacitor C o0 The circuit is turned on, and the second DC capacitor C n0 Output power to the voltage balancing component 21, and the voltage balancing component 21 outputs power to the output capacitor C o0 .

[0063] In practical applications, by outputting a driving signal to the voltage balancing component 21, the corresponding loop is turned on, so that the voltage self-balancing module operates alternately in two working conditions, thereby achieving the first DC capacitor C p0 , the second DC capacitor C n0 , output capacitor C o0 The voltage between them is balanced to achieve the purpose of voltage balance within the module.

[0064] In a specific embodiment, the voltage balancing component 21 includes a first resonant branch, a second resonant branch, a first half-bridge submodule, a second half-bridge submodule, and a third half-bridge submodule;

[0065] The first half-bridge submodule and the first DC capacitor C p0 in parallel;

[0066] The second half-bridge submodule and the output capacitor C o0 in parallel;

[0067] The third half-bridge submodule and the second DC capacitor C n0 in parallel;

[0068] The first half bridge submodule, the second half bridge submodule, and the third half bridge submodule are connected in series;

[0069] The first resonant branch is connected to the first half-bridge submodule and the second half-bridge submodule respectively;

[0070] The second resonant branch is connected to the second half-bridge sub-module and the third half-bridge sub-module respectively.

[0071] It should be noted that both the first resonant branch and the second resonant branch adopt LC resonant circuits. The first resonant branch can be connected to the first half-bridge submodule, the second half-bridge submodule and the first DC capacitor C p0 A loop is formed, or through the first half-bridge submodule, the second half-bridge submodule and the output capacitor C o0 The second resonant branch is similar.

[0072] Specifically, in one working mode, the first resonant branch, the first half-bridge submodule, the second half-bridge submodule and the first DC capacitor C p0 The circuit is turned on, so that the first DC capacitor C p0 Output electric energy to the first resonant branch, and the second resonant branch, the second half-bridge submodule, the third half-bridge submodule and the output capacitor C o0 The loop is turned on, so that the second resonant branch outputs electrical energy to the output capacitor C o0 In another working mode, the first resonant branch, the first half-bridge submodule, the second half-bridge submodule and the output capacitor C o0 The loop is turned on, so that the first resonant branch outputs electrical energy to the output capacitor C o0 , and the second resonant branch, the second half-bridge submodule, the third half-bridge submodule and the second DC capacitor C n0 The circuit is turned on, so that the second DC capacitor C n0 Output electric energy to the second resonant branch.

[0073] In a specific embodiment, see Figure 3 , the first resonant branch includes a first resonant inductor L rp0 and the first resonant capacitor C rp0 ; The first resonant inductor L rp0 One end and the first resonant capacitor C rp0 One end of the series connection;

[0074] The first resonant capacitor C rp0 The other end is connected to the first half-bridge submodule;

[0075] The first resonant inductor L rp0 The other end is connected to the second half-bridge sub-module.

[0076] Furthermore, the second resonant branch includes a second resonant inductor L rn0 and the second resonant capacitor C rn0 ; The second resonant inductor L rn0 One end of the second resonant capacitor C rn0 One end of the series connection;

[0077] The second resonant capacitor C rn0 The other end is connected to the second half-bridge submodule;

[0078] The second resonant inductor L rn0 The other end is connected to the third half-bridge sub-module.

[0079] Furthermore, the first half-bridge submodule includes a first semiconductor power switch device S 01 and the second semiconductor power switch device S 02 ;

[0080] The first semiconductor power switch device S 01 The first end of the first DC capacitor C p0 One end of the first semiconductor power switch device S 01 The second end of the first resonant capacitor C rp0 The other end of the second semiconductor power switch device S 02 A first end is connected;

[0081] The second semiconductor power switch device S 02 The second end of the second half-bridge sub-module and the first DC capacitor C p0 The other end of the connection.

[0082] Furthermore, the second half-bridge submodule includes a third semiconductor power switch device S 03 and a fourth semiconductor power switch device S 04 ;

[0083] The third semiconductor power switch device S 03 The first end of the output capacitor C o0 One end of the second semiconductor power switch device S 02 The second end of the third semiconductor power switch device S 03 The second end of the first resonant inductor L rp0 The other end of the second resonant capacitor C rn0 The other end of the fourth semiconductor power switch device S 04 A first end is connected;

[0084] The fourth semiconductor power switch device S 04 The second end is connected to the third half-bridge sub-module and the output capacitor C o0 The other end of the connection.

[0085] Furthermore, the third half-bridge submodule includes a fifth semiconductor power switch device S 05 and a sixth semiconductor power switch device S 06 ;

[0086] Fifth semiconductor power switch device S 05 The first end of the second DC capacitor C n0 one end of the fourth semiconductor power switch device S04 The second end of the fifth semiconductor power switch device S 05 The second end of the second resonant inductor L rn0 The other end of the sixth semiconductor power switch device S 06 A first end is connected;

[0087] The sixth semiconductor power switch device S 06 The second end of the second DC capacitor C n0 The other end of the connection.

[0088] This embodiment takes the structure of the input module as an example to illustrate the internal structure of the voltage self-balancing module as follows.

[0089] like Figure 3 As shown, the first resonant capacitor C rp0 and the first resonant inductor L rp0 series, and the first resonant capacitor C rp0 Connected to the first semiconductor power switch device S 01 and the second semiconductor power switch device S 02 The connection point of the first resonant inductor L rp0 Connected to the third semiconductor power switch device S 03 and a fourth semiconductor power switch device S 04 The connection point of the second resonant capacitor C rn0 The second resonant inductor L rn0 series, and the second resonant capacitor C rn0 and the first resonant inductor L rp0 , the third semiconductor power switch device S 03 and a fourth semiconductor power switch device S 04 The second resonant inductor L rn0 Connected to the fifth semiconductor power switch device S 05 and a sixth semiconductor power switch device S 06 The first semiconductor power switch device S 01 and the second semiconductor power switch device S 02 After connecting in series with the first DC capacitor C p0 In parallel, the third semiconductor power switch device S 03 and a fourth semiconductor power switch device S 04 After connecting in series with the output capacitor C o0 In parallel, the fifth semiconductor power switch device S 05 and a sixth semiconductor power switch device S 06 After connecting in series with the second DC capacitor C n0 In parallel, the second semiconductor power switch device S 02 and a third semiconductor power switch device S03 In series, the fourth semiconductor power switch device S 04 The fifth semiconductor power switch device S 05 Series connection.

[0090] Among them, the first semiconductor power switch device S 01 To the sixth semiconductor power switch device S 06 It can be divided into two groups, one of which is the first semiconductor power switch device S 01 , the third semiconductor power switch device S 03 , the fifth semiconductor power switch device S 05 and a sixth semiconductor power switch device S 06 ; The other group is the second semiconductor power switch device S 02 , the fourth semiconductor power switch device S 04 , the sixth semiconductor power switch device S 06 Two groups of semiconductor power switching devices are connected with T s / 2 time rotation conduction, where T s is the time of a switching cycle of a semiconductor power switch device. Therefore, the entire working process of the input module can be divided into two working modes, as follows: Figure 4 The corresponding conduction pulse and the voltage and current waveforms of the resonant circuit are shown as Figure 5 shown.

[0091] Mode 1: When in [0-T s / 2], when t=0, the first semiconductor power switch device S 01 , the third semiconductor power switch device S 03 , the fifth semiconductor power switch device S 05 The corresponding working circuit is as follows: Figure 4 (a) The first resonant inductor L rp0 , the first resonant capacitor C rp0 , the first semiconductor power switch device S 01 , the first DC capacitor C p0 , the third semiconductor power switch device S 03 The second resonant capacitor C rn0 , the third semiconductor power switch device S 03 , output capacitor C o0 , the fifth semiconductor power switch device S 05 , the second resonant inductor L rn0 A resonant circuit n is formed.

[0092] Among them, the resonant circuit p is from the first DC capacitor C p0 Absorbs energy, making the resonant current i rp0Starting from zero, the resonant capacitor C rp0 The voltage v rp0 It starts to increase from the minimum value. The resonant circuit n to the output capacitor C o0 Release energy, so that the resonant current i rn0 It also starts to resonate from zero reverse direction and makes the resonant capacitor C rn0 The voltage v rn0 It starts to decay from the maximum value. When this mode ends, the resonant current i rp0 and i rn0 Both return to 0, the resonant capacitor C rp0 The voltage v rp0 increases to its maximum value, and the resonant capacitor C rn0 The voltage v rn0 Attenuated to the minimum value, the expressions of current and voltage during the entire mode period are:

[0093]

[0094]

[0095] Among them, t0 is the mode start time, ω rp0 ,ω rn0 are the resonant frequencies of resonant circuit p and resonant circuit n, respectively, cp0 is the first DC capacitor C p0 The voltage, v cn0 is the second DC capacitor C n0 voltage.

[0096] Mode 2: When in [T s / 2-T s ],t=T s / 2, the second semiconductor power switch device S 02 , the fourth semiconductor power switch device S 04 , the sixth semiconductor power switch device S 06 The corresponding working circuit is as follows: Figure 4 (b) The first resonant inductor L rp0 , the first resonant capacitor C rp0 , the second semiconductor power switch device S 02 , output capacitor C o0 , the fourth semiconductor power switch device S 04 The second resonant capacitor C rn0 , the fourth semiconductor power switch device S 04 , the second DC capacitor C n0 , the sixth semiconductor power switch device S 06 , the second resonant inductor L rn0 A resonant circuit n is formed.

[0097] The resonant circuit p-to-output capacitor C o0 Release energy, making the resonant current i rp0 Starting from zero reverse resonance changes, the voltage v of the resonant capacitor rp0 The resonant circuit n starts to decay from the maximum value. n0 Absorb energy, making the resonant current i rn0 Starting from zero, the resonant capacitance C n0 The voltage v rn0 The minimum value begins to increase. At the end of this mode, the resonant current i rp0 and i rn0 All return to 0, the resonant capacitor C rp0 The voltage v rp0 attenuates to the minimum value, and the resonant capacitor C n0 The voltage v rn0 Increase to maximum value.

[0098] Based on the above analysis, we can see that the resonance characteristics make the voltages of the three DC capacitors automatically balanced, so the voltage V dc1 is the secondary port V bus Similarly, Figure 4 The topology is extended to a multi-module topology, that is, for Figure 3 For any 3RSC-x module (x=1,2,…n), the resonance characteristic makes the primary port voltage V dcx Both are three times the secondary port voltage. Figure 3 Each DAB module is connected in parallel to the output capacitor C of 3RSC-0. o0 At, the input voltage is V bus , this voltage is transformed by DAB-x and becomes the voltage of the secondary port of 3RSC-x, which is C ox Due to the resonant characteristics of each 3RSC module, C px With C nx The voltage of C ox Therefore, by controlling the output voltage of DAB-x to be equal, the primary and secondary voltages of 3RSC-x can be controlled to be equal. The entire topology has an autocoupled structure, so some energy can be transferred from the DC bus V bus The energy transmitted by DAB can be transferred to other 3RSC modules to achieve energy balance between modules. Therefore, by controlling the energy transmitted by DAB, the voltage control of other 3RSC modules can be achieved, thereby achieving overall voltage balance.

[0099] In one example, the first semiconductor power switch device S 01 To the sixth semiconductor power switch device S 06An IGBT tube may be selected. Among them, the first semiconductor power switch device S 01 The first end of the second semiconductor power switch device S 02 The first end of the third semiconductor power switch device S 03 The first end of the fourth semiconductor power switch device S 04 The first end of the fifth semiconductor power switch device S 05 The first end of the sixth semiconductor power switch device S 06 The first end of each semiconductor power switch device S is a collector. 01 The second end of the second semiconductor power switch device S 02 The second end of the third semiconductor power switch device S 03 The second end of the fourth semiconductor power switch device S 04 The second end of the fifth semiconductor power switch device S 05 The second end of the sixth semiconductor power switch device S 06 The second end of each is an emitter.

[0100] In order to further illustrate the effect achieved by the modular DC transformer provided in the embodiment of the present invention, a simulation application example will be described below.

[0101] In this application example, simulation software (such as MATLAB / Simulink) is used to build a corresponding simulation model based on the topological structure of the modular DC transformer provided in the above embodiment, and the simulation model is experimentally verified. The simulation parameters are shown in Table 1 below. There are 5 voltage self-balancing modules 3RSC.

[0102] The input voltage is set to 6kV, the output voltage is 35kV, the transmission power is 5MW, the switching frequency of each semiconductor power switch device is 10kHz, and in each voltage self-balancing module, the first DC capacitor C p0 , the second DC capacitor C n0 , output capacitor C o0 The value of the first resonant capacitor C is 1mF. rp0 and the second resonant capacitor C rn0 The value of is 50uF, the first resonant inductor L rp0 , the second resonant inductor L rn0 The value is 20uH.

[0103] Table 1 DC transformer simulation parameters

[0104]

[0105] Figure 6 The simulation waveform of the 3RSC-0 module connected to the input side is shown.rp0 and i rn0 are the currents of resonant circuit p and resonant circuit n, respectively, and v rp0 and v rn0 They are the first resonant capacitor C rp0 and the second resonant capacitor C rn0 The voltage waveform, v Co0 、v Cp0 、v Cn0 are the voltages of the output capacitor, the first DC capacitor, and the second DC capacitor in the 3RSC-0 module respectively. Figure 6 It can be seen that i rp0 and i rn0 The waveforms are complementary, switching to the output capacitor C 0x When transferring energy, the voltages of the output capacitor, the first DC capacitor, and the second DC capacitor are all stabilized at 2 kV, which proves that the voltage self-balancing module 3RSC has good voltage self-balancing capability.

[0106] exist Figure 7 In, V i1 ~V i4 They are the primary side voltages of the four modules 3RSC-1~3RSC-4. It can be seen that V i1 ~V i4 The primary side voltage of the 3RSC modules is stable at 7.25kV. In this topology, the sum of the primary side voltages of all 3RSC modules is 7.25×4+6=35kV, that is, the high-voltage side voltage V dc2 Achieved 35kV output.

[0107] Combined with the above analysis, it can be seen that in the modular DC transformer provided in the embodiment of the present invention, the voltage self-balancing module can realize automatic voltage balancing, and the voltage balancing between modules can be realized between the transmission modules. Therefore, the modular DC transformer provided by the present invention can realize voltage balancing more conveniently, reduce the difficulty of voltage balancing, improve the energy transmission efficiency, and solve the problem of complex voltage balancing existing in the existing modular DC transformer.

[0108] See also Figure 8 , an embodiment of the present invention further provides a control system, comprising a controller 1, and a modular DC transformer 2 as in any of the above embodiments;

[0109] The controller 1 is connected to the DAB module 23 and the voltage self-balancing module 22 in the modular DC transformer 2 respectively.

[0110] It should be noted that the controller 1 is connected to the switch device in the full bridge of the DAB module 23, and is used to control the on and off of the switch device in the DAB module 23. In practical applications, the controller 1 can be used to output control signals to the DAB module 23 and the voltage self-balancing module 22, respectively, to adjust the output voltage of the DAB module 23 and the working mode of the voltage self-balancing module 22.

[0111] In a specific embodiment, the controller 1 is connected to the first half-bridge sub-module, the second half-bridge sub-module, and the third half-bridge sub-module in the voltage self-balancing module 22 .

[0112] It should be noted that, in actual applications, the controller 1 is connected to the control end of each semiconductor power switch device in the first half-bridge sub-module to the third half-bridge sub-module, so that by outputting a drive signal to the control end of each semiconductor power switch device, each conductor power switch device can be alternately turned on, so that the voltage self-balancing module operates alternately in two working modes.

[0113] When each semiconductor power switch device uses an IGBT tube, the control end of each semiconductor power switch device is a gate.

[0114] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0115] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0116] It should also be noted that in the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

[0117] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modular DC transformer, characterized in that: It includes at least two voltage self-balancing modules and at least one DAB module; Using one of the voltage self-balancing modules as an input module, the primary port of the input module is connected to the low voltage side, and the secondary port of the input module is connected in parallel with the DAB module; The voltage self-balancing module of the non-input module is used as a transmission module, and the primary port of the transmission module is connected in series with the primary port of the input module for connecting to the high-voltage side; the secondary port of the transmission module is connected to the DAB module; The voltage self-balancing module is used to balance the voltage inside the module.

2. The modular DC transformer according to claim 1, characterized in that: The voltage self-balancing module includes: a voltage balancing component, a first DC capacitor, a second DC capacitor and an output capacitor; The first DC capacitor, the second DC capacitor, and the output capacitor are connected in series in sequence to form the primary port; the two ends of the output capacitor are the secondary ports; The voltage balancing component is respectively connected to both ends of the first DC capacitor, both ends of the output capacitor, and both ends of the second DC capacitor, and is used to balance the voltage of the first DC capacitor, the voltage of the second DC capacitor, and the voltage of the output capacitor.

3. The modular DC transformer according to claim 2, characterized in that: The voltage equalization component includes a first resonant branch, a second resonant branch, a first half-bridge submodule, a second half-bridge submodule, and a third half-bridge submodule; The first half-bridge sub-module is connected in parallel with the first DC capacitor; The second half-bridge submodule is connected in parallel with the output capacitor; The third half-bridge sub-module is connected in parallel with the second DC capacitor; The first half-bridge submodule, the second half-bridge submodule, and the third half-bridge submodule are connected in series; The first resonant branch is connected to the first half-bridge sub-module and the second half-bridge sub-module respectively; The second resonant branch is connected to the second half-bridge sub-module and the third half-bridge sub-module respectively.

4. The modular DC transformer according to claim 3, characterized in that: The first resonant branch includes a first resonant inductor and a first resonant capacitor; one end of the first resonant inductor and one end of the first resonant capacitor are connected in series; The other end of the first resonant capacitor is connected to the first half-bridge sub-module; The other end of the first resonant inductor is connected to the second half-bridge sub-module.

5. The modular DC transformer according to claim 4, characterized in that: The second resonant branch includes a second resonant inductor and a second resonant capacitor; one end of the second resonant inductor and one end of the second resonant capacitor are connected in series; The other end of the second resonant capacitor is connected to the second half-bridge sub-module; The other end of the second resonant inductor is connected to the third half-bridge sub-module.

6. The modular DC transformer according to claim 5, characterized in that: The first half-bridge submodule includes a first semiconductor power switch device and a second semiconductor power switch device; The first end of the first semiconductor power switch device is connected to one end of the first DC capacitor; the second end of the first semiconductor power switch device is connected to the other end of the first resonant capacitor and the first end of the second semiconductor power switch device respectively; The second end of the second semiconductor power switch device is connected to the second half-bridge sub-module and the other end of the first DC capacitor respectively.

7. The modular DC transformer according to claim 6, characterized in that: The second half-bridge submodule includes a third semiconductor power switch device and a fourth semiconductor power switch device; The first end of the third semiconductor power switch device is respectively connected to one end of the output capacitor and the second end of the second semiconductor power switch device; the second end of the third semiconductor power switch device is respectively connected to the other end of the first resonant inductor, the other end of the second resonant capacitor, and the first end of the fourth semiconductor power switch device; The second end of the fourth semiconductor power switch device is connected to the third half-bridge sub-module and the other end of the output capacitor respectively.

8. The modular DC transformer according to claim 7, characterized in that: The third half-bridge submodule includes a fifth semiconductor power switch device and a sixth semiconductor power switch device; The first end of the fifth semiconductor power switch device is respectively connected to one end of the second DC capacitor and the second end of the fourth semiconductor power switch device; the second end of the fifth semiconductor power switch device is respectively connected to the other end of the second resonant inductor and the first end of the sixth semiconductor power switch device; The second end of the sixth semiconductor power switch device is connected to the other end of the second DC capacitor.

9. A control system, characterized in that: It comprises a controller and a modular DC transformer as claimed in any one of claims 1 to 8; The controller is respectively connected to the DAB module and the voltage self-balancing module in the modular DC transformer.

10. The control system according to claim 9, characterized in that: The controller is connected to the first half-bridge sub-module, the second half-bridge sub-module, and the third half-bridge sub-module in the voltage self-balancing module.

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